Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $38.79   5.154%   $40.7892   $40.79   $40.80   $40.80  
  Purchase #2 $173.31   11.592%   $193.4001   $193.40   $193.40   $193.40  
  Purchase #3 $49.49   9.222%   $54.054   $54.05   $54.05   $54.10  
  Purchase #4 $174.35   12.427%   $196.0165   $196.02   $196.00   $196.00  
  Purchase #5 $57.69   5.126%   $60.6472   $60.65   $60.65   $60.60  
  Purchase #6 $156.56   13.278%   $177.348   $177.35   $177.35   $177.30  
  Purchase #7 $135.97   4.211%   $141.6957   $141.70   $141.70   $141.70  
  7 purchase totals = $786.16       $863.9507   $863.96   $863.95   $863.90